The calcium deficiency usually refers to the lack of calcium in the bones and whether osteoporosis is induced due to the lack of calcium in the bones. Blood calcium refers to the free calcium ions in the blood serum, 99.99% of calcium in the human body is in the bones, only a very small part of dissolved in the blood, play the role of calcium ions to promote nerve excitation and heart contraction, blood calcium does not represent the lack of calcium deficiency. The body eats and the gastrointestinal tract absorbs calcium from food into the blood, and then the calcium in the blood is only deposited on the bone surface by osteogenic cell calcification under the regulation of human hormones and synthesis. Therefore, problems in any of the above processes can cause abnormalities in the deposition of calcium in the bones, resulting in osteoporosis. Blood calcium, also known as serum calcium, reflects the electrolytes in the body from the free calcium ions in the blood to reflect whether the electrolytes are normal or not, but it lacks a certain degree of evaluation for determining whether there is calcium deficiency. In order to determine whether a person is calcium deficient, a systematic examination of bone mineral density, calcium hormone levels and bone metabolism markers should be performed. If a person is in a calcium deficiency state, what kind of level is he or she in? Therefore, the results of blood calcium alone are not sufficient to judge whether the body is deficient in calcium.